Field of the Invention
The present invention relates to a positive electrode active material for nonaqueous electrolyte secondary batteries, such as lithium ion secondary batteries.
Description of the Related Art
In recent years, miniaturization and high functionalization of mobile devices such as mobile phones and note-type PCs have been in progress. For the driving power source of those mobile devices, nonaqueous electrolyte secondary batteries, such as lithium ion secondary batteries, have been used. The nonaqueous electrolyte secondary batteries have high operating voltage and thus have the advantage of higher energy density than those of other secondary batteries. Due to this advantage, the nonaqueous electrolyte secondary batteries have started being applied in larger machinery such as electric vehicles.
As a major example of positive electrode active materials for nonaqueous electrolyte secondary batteries, lithium cobalt oxide (LiCoO2) has been put into practical use. The nonaqueous electrolyte secondary batteries which use lithium transition metal composite oxides having a layer structure, such as lithium cobalt oxide, as the positive electrode active materials have average operating voltage of approximately 3.5 V. Meanwhile, with the use of a lithium transition metal composite oxide having a spinel structure, such as lithium manganate (LiMn2O4), as a positive electrode active material, a nonaqueous electrolyte secondary battery with the average operating voltage of 4 V or greater can be obtained. In particular, when LiNi0.5Mn1.5O4 is used, the average operating voltage can be approximately 4.5 V.
There has been technology in the lithium transition metal composite oxide having a spinel structure, for substituting a part of manganese with nickel, other elements, or nickel and other elements according to the purpose.
JP 2003-197194A discloses a technology that substitutes a part of manganese in a lithium-manganese composite oxide having a spinel structure with nickel or the like and/or with titanium or the like to enhance energy density of a secondary battery.
WO2012/077472 discloses a technology that substitutes a part of manganese in a lithium-manganese composite oxide having a spinel structure with nickel and chromium and with magnesium or the like to improve cycle characteristics of a secondary battery.
JP 2012-033279A discloses a technology that uses, as a positive electrode, a lithium-nickel-manganese oxide having a particular range of specific surface area to prevent decrease in capacity of a secondary battery, which uses a lithium-titanium oxide as a negative electrode, during fast charging. As an example of the lithium-nickel-manganese oxide, LiNi0.4Cr0.05Al0.05Mn1.4Ti0.1O4 has been disclosed.